Problem: $-\dfrac{4}{12} - \dfrac{9}{3} = {?}$
Solution: $ = - {\dfrac{4 \times 1}{12 \times 1}} - {\dfrac{9 \times 4}{3 \times 4}} $ $ = - {\dfrac{4}{12}} - {\dfrac{36}{12}} $ $ = - \dfrac{{4} - {36}}{12} $ $ = -\dfrac{40}{12}$